This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The T. brucei flagellum is a multi-component, multifunctional organelle critical for pathogenesis. This flagellum contains not only the classic "9+2" axoneme but also a crystalline paraflagellar rod (PFR). The biological interest in this project is the structural organization of the two major structural components of PFR which have been characterized, PFR1 and PFR2 at 69KD and 73KD, respectively. They appear by sequence analysis to consist largely of coiled-coil motifs. Depletion of one PFR protein by RNA interference did not affect parasite growth or division nor formation of the axoneme. However, it completely abolished the assembly of the PFR, resulting in defects in cell motility and infectivity. We plan to use cryo-ET to study the structural organization of this complex organelle.